| Subwoofers and the Inverse Square Law | | Amplifier Low Frequency Capability |
| Even though frequencies below 200Hz are relatively omni-directional, | Many 70.7V / 100V power amplifiers on the market today are from the |
| listeners can still "localize" the subwoofer from the volume produced. To | era when business music systems extending down to only 100Hz were |
| avoid "hot spots" it may be necessary to use two or more subwoofers | widely accepted. These less expensive amplifiers are not capable of |
| tapped at a lower setting spread throughout the room instead of a single | driving today's high fidelity systems that require sound below 100Hz. |
| subwoofer tapped at maximum wattage. | | | When specifying the Atlas Sound FAPSUB, which operates well below |
| Ratio of Subwoofers to Full Range Speakers | | 100Hz, it is VERY IMPORTANT to use a power amplifier capable of full |
| | output down to and below the lowest frequency going INTO the amp, |
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| Due to the many potential variables, it is difficult to give accurate sugges- | which is often around 50Hz. An amplifier with low-frequency capability is |
| absolutely crucial whenever the system includes a subwoofer and is very |
| tions on system design. It is important for the system designer to look at |
| important for today's high fidelity business music systems. |
| the required SPL at ear level, ambient noise in the room, speaker / trans- |
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| former efficiency, and transformer insertion loss to determine the num- | Architect & Engineer Specficiations |
| ber of speakers and amplifier power required. In 70.7V / 100V systems, | | |
| care should be taken so the total speaker power taps do not exceed the | The loudspeaker system shall be Atlas Sound FAPSUB or approved equal. |
| amplifier's 70.7V output capability. | | | System shall include a high performance 8" subwoofer loudspeaker, |
| | | (preliminary) |
| The following “rule of thumb” information and examples are offered to | ported bass reflex enclosure, and stud mount grille for conventional ceil- |
| provide a starting point for system design. | | | ing installation. |
| For “good” low frequency augmentation in a full range system (all full | Frequency response for the system shall be 45Hz – 120Hz (±10dB) and |
| range speakers and FAPSUBs on the same amplifier), a single FAPSUB | the sensitivity shall be 89dB (SPL at 1W / 1M). |
| should be used for every four full range speakers. | | | Loudspeaker shall be comprised of an 8" low frequency cone type driver. |
| For “excellent” low frequency augmentation in a full range system | Magnet shall be a minimum of 20oz (580g) and the voice coil diameter |
| (all full range speakers and FAPSUBs on the same amplifier), a single | shall be 1". Transformer shall be 70.7V with p ima taps at 1.9, 3.8, 7.5, |
| FAPSUB should be used for every two full range speakers. | | 15, 30, and 60 watts. A front mount tap selector switch shall be included. |
| | | | | This switch shall have tr nsfo mer byp ss setting for 8Ω / direct cou- |
| Amplifier Limitations | | | | pled operation |
| Even with the extreme efficiency of the FAPSUB it will not overcome the | Enclosure shall be a deep dr wn, 937 in3, steel enclosure design. To |
| limitations of an underpowered system. Be sure to allow sufficient head- | facilitate connection in co duit systems, enclosure shall be equipped |
| room by using basic system design parameters in choosing an amplifier. | with an access pa el coveri g a recessed terminal cup. This cover shall |
| | | | | provide a comb at on 3⁄4" (19mm i side diameter) / 1" (25mm inside diam- |
| Example | Small Sports Bar | | | eter) knock-out on the s de access a d a top access compression fitting |
| Square Feet | 1,500 | | | / strain relief to fac l tate flex ble conduit up to 22mm outside diameter |
| Ceiling Height | 9' | | | or 1" (25mm ns de d ameter) conduit when the compression fitting is |
| Peak Ambient Noise Level | 75 dB | | | re | oved. |
| Program | Digital Music | | | External wiring shall be accomplished via a removable, lockable wiring |
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| Full Range Speakers | | | | connector w th screw-down terminals to provide both secure wire |
| | | | | ter | nat on and prewiring capability before loudspeaker installation. |
| Eight Atlas Sound FAP42T speakers tapped at 4 watts each (32 watts | The 4 po e ock ng Phoenix Style / Euro connector shall facilitate in/out |
| total) will provide 90dB on axis at 3.5' ear height (15dB above ambient). |
| connect ons and shall be located in the recessed area behind the conduit |
| 13.5' spacing between speakers provides minimum overlap coverage at |
| acc | ss panel. |
| 4kHz. | | | |
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| Subwoofers | | | | S ismic support eye shall be provided on top of enclosure for additional |
| | | | susp nsion point when used in drop tile ceilings. Construction of enclo- |
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| Two Atlas Sound FAPSUB subwoofers tapped at 30 watts each (60 watts | sure shall be a minimum of 18-gauge deep drawn galvanized metal. |
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| total) will fill out the low frequencies at 8dB above the level of the full | The system shall include a support backing plate to reinforce the ceil- |
| range speakers. If boundary loaded into one corner of the | oom the level | ing material and tile support rails for use on either 2' x 4' (609mm x |
| will be increased another 6dB (14dB above the full range s | eakers). | 1219mm) or 2' x 2' (609mm x 609mm) suspended ceiling tiles. This |
| Total Wattage: 92 watts x 1.3 Multiplier for headroom) = 119.6 watts | assembly can all be installed from beneath the ceiling tile. |
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| Amplifier Power Suggested: 120 Watts Atlas Sound AA120 | Overall front face diameter shall not exceed 153⁄4" (400mm); overall depth |
| | | | | from the bottom of the ceiling shall not exceed 123⁄4" (323mm). Grilles |
